1. Field of the Invention
The present invention relates to a DC power source unit that can selectively charge a battery pack, which is used as a power source for a cordless power tool, and supply DC power to the cordless power tool through an adaptor shaped like the battery pack.
2. Description of the Related Art
Cordless power tools are convenient because they can be used anywhere without being restricted by the length of a power cable. However, because the capacity of the battery is limited, the length of time that the power tool can be used is also limited. U.S. Pat. No. 6,172,860 (corresponding to DE-OS 19844426 A1) and Japanese Patent Publication (A) No. 11-101836 (corresponding to a co-pending U.S. application Ser. No. 09/478,798) disclose DC power source units that can be used for cordless power tools, in which DC power is continuously supplied to the power tool via an adapter. The DC power source unit can be used along with the battery pack.
Japanese Patent Publication (A) No. 2000-184614discloses a DC power source unit with a battery pack charging function, which will be described in more detail while referring to FIG. 1. A power tool 20 is operable with a battery pack 19 that has a shape insertable into a handgrip of the power tool 20. The power tool 20 is also operable with an adapter 18 that has a substantially same shape as the battery pack 19. The adapter 18 is connected to a DC power source unit 17 via a cord 22, and the DC power source unit 17 is connected, while in use, to a commercial AC power source via a cord 15 and a plug 14. The DC power source unit 17 supplies DC power to the power tool 20 when the adapter 18 is used instead of the battery pack 19.
The DC power source unit 17 is accommodated in a rectangular box having a top wall, side walls, and a bottom wall. The top wall is formed with a battery pack insertion hole 8, into which the battery pack 19 is inserted for charging.
The DC power source unit 17 is being operated not only during charging the battery pack 19 but also during supplying DC power to the power tool 20. Accordingly, a large amount of heat is generated from the circuit components contained in the DC power source unit 17, however, no proposal has ever been made for dissipating the heat.
The most conceivable solution for dissipating the heat and cooling the circuit components in the DC power source unit would be providing a cooling system. If, as shown in FIG. 2, cooling air inlet holes 3 are formed in one side wall of the rectangular box 7, air outlet holes 21 in the opposite side wall, and a cooling fan 1 is fixed to the inner surface of the side wall in which the air outlet holes 21 are formed, then circuit components 25 mounted on fins 2 would be cooled by air introduced from the air inlet holes 3
However, the air flows through the box 7 in different patterns depending upon whether or not the battery pack 19 is inserted into the insertion hole 81 because terminal holes 4 are formed in positions below the battery pack insertion hole 8. When the battery pack 19 is not inserted into the insertion hole 8, the air Introduced through the battery pack insertion hole 8 and the terminal holes 4 flows in patterns 6 out through the air outlet holes 21 in addition to the air introduced through the air inlet holes 3 and flows in pattern 5.
On the other hand, insertion of the battery pack 19 into the insertion hole 8 closes the terminal holes 4, thereby interrupting air flowing in patterns 6. In this condition, air flowing in patterns 5 effectively cools down the circuit components 25. The air flowing in patterns 6 disturbs the air flowing in patterns 5 and thus lowers the cooling effect attained by the air flowing in patterns 5.
In view of the foregoing, it is an object of the invention to assure cooling of circuit components contained in a DC power source unit regardless of whether or not a battery pack is inserted into an insertion hole.
To achieve the above and other objects, there is provided a DC power source unit that is capable of maintaining air flow generated by a cooling fan unchanged regardless of whether or not the battery pack is accommodated in the battery pack insertion hole. The housing is formed with an air inlet portion and an air outlet portion, preferably in a confronting relation. The housing is further formed with a battery pack insertion hole. There is provided means for defining a battery pack accommodating space for accommodating a battery pack inserted from the battery pack insertion hole. A substrate is disposed inside the housing. Circuit components are mounted on the substrate and disposed in the main inner space of the housing that is different from the battery pack accommodating space. The circuit components are mutually connected together to generate charging power to be supplied to the battery pack and DC power to be supplied via an adapter to the power tool for driving. The battery pack is used as an alternative power source of the power tool and charged by the charging power when inserted from the battery pack insertion hole and accommodated in the battery pack insertion space. Air flow generating means, such as a cooling fan, is disposed in the main space for generating air flow to cool down the circuit components. Air flow maintaining means is provided for maintaining the air flow at substantially constant regardless of whether or not the battery pack is accommodated in the battery pack accommodating space. The air flow maintaining means maintains a speed of the air flow at substantially constant and also maintains a volume of air per a unit time at substantially constant.